Influence of environmental conditions on the glass transition temperature of epoxy used for strengthening applications

Abstract

Abstract This work investigates the effect of environmental conditions on the glass transition temperature (Tg) of three different epoxy adhesives for structural application by exposure to accelerated ageing regimes up to 240 days. Despite current standards for differential scanning calorimetry (DSC) recommending the assessment of Tg in the second heating cycle, this study focusses on the first heating cycle because it is more representative of the real in-situ conditions. Results reveal that the use of the second heating cycle often leads to an overestimated definition of Tg. DSC trends are partially confirmed by dynamic mechanical analysis (DMA). Indeed, in the case of epoxy exposed to wet conditions, standard DMA seems to be less sensitive than DSC in detecting the detrimental effect of the water uptake on Tg. For design purposes, the use of safety margins in service conditions, as recommended in ACI 440.2R-17 and fib Bulletin 90, is discussed.